Fire safety study on high-flow nasal oxygen in shared-airway surgeries with diathermy and laser: simulation based on a physical model.

High-flow nasal oxygen (HFNO) has been used in "tubeless" shared-airway surgeries but whether HFNO increased the fire hazard is yet to be examined. We used a physical model for simulation to explore fire safety through a series of ignition trials. An HFNO device was attached to a 3D-printed nose with nostrils connected to a degutted raw chicken. The HFNO device was set at twenty combinations of different oxygen concentration and gas flow rate. An electrocautery and diode laser were applied separately to a fat cube in the cavity of the chicken. Ten 30 s trials of continuous energy source application were conducted. An additional trial of continuous energy application was conducted if no ignition was observed for all the ten trials. A total of eight short flashes were observed in one hundred electrocautery tests; however, no continuous fire was observed among them. There were thirty-six events of ignition in one hundred trials with laser, twelve of which turned into violent self-sustained fires. The factors found to be related to a significantly increased chance of ignition included laser application, lower gas flow, and higher FiO. The native tissue and smoke can ignite and turn into violent self-sustained fires under HFNO and continuous laser strikes, even in the absence of combustible materials. The results suggest that airway surgeries must be performed safely with HFNO if only a short intermittent laser is used in low FiO.